Handling's gone pearshaped!!
07-04-2002, 03:30 PM
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Drifting
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Handling's gone pearshaped!!
Had new tyres fitted on the rear today - replace really worn (great grip in the dry!!)255/40/17 Falkens with Toyo Proxes TS-1, also 255/40/17. I left the existing Falkens on the front (yes Adrian, don't say it, but my service just cost me over £1k, so things are tight with the wife at the mo!!!).
Anyway, I don't think its my imagination, but the front of the car now sems really light & twitchy, like there is no weight on the tyres. Its really vague and drifty at just 80 mph. Last week, I had it at 125 mph and it was only just getting a bit vague.
I'm not sure if its relevant, but though I think its stock suspension wise, hte rear wheel to arch clearance is only 1", but its 2.5" at the front of the car.
I've not hit any kerbs or bumps, and I watched the guys put the tyres on - they didn't touch the front.
Help!!!!
Anyway, I don't think its my imagination, but the front of the car now sems really light & twitchy, like there is no weight on the tyres. Its really vague and drifty at just 80 mph. Last week, I had it at 125 mph and it was only just getting a bit vague.
I'm not sure if its relevant, but though I think its stock suspension wise, hte rear wheel to arch clearance is only 1", but its 2.5" at the front of the car.
I've not hit any kerbs or bumps, and I watched the guys put the tyres on - they didn't touch the front.
Help!!!!
07-04-2002, 07:25 PM
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Hello John,
Well, as you probably know, most people will recommend against mixing different model tires, front & rear. Regardless, I recently installed RE-730s on the rear of my car, while keeping my half-worn RE-71s up front. Honestly, it doesn't cost anymore money (just time) to go back and replace the fronts, if you can't tolerate the performance. You just need to be smart enough to not push the car too hard while evaluating the car's handling with the mixed tires (just like you do after installing new tires). And, besides being cheap, I wanted to experience first-hand how a 964 handles with mixed front/rear tires.
Now, my car (and probably your own) always handles a bit flaky immediately after new tires are installed. However, it's been over 1k miles since the new RE-730s were installed, and I'm still not happy with how the car's front-end feels at freeway speeds. And, the back-end feels too squirrely. So, it's time to bite the bullet, and order up a set of RE-730s for the front. Experiment over.
Here's a link to a relevant thread from the 993 board:
<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=3&t=003101&p=" target="_blank">Mixing Different Tire Models?</a>
Also, I believe Steve Weiner goes so far as to recommend that you replace all four tires whenever you buy new tires, regardless of whether you'll be installing different model tires, or how much tread may be on (for example) the front tires. Unfortunately, I was unable to locate the thread where I remember Steve W. making this recommendation.
Well, as you probably know, most people will recommend against mixing different model tires, front & rear. Regardless, I recently installed RE-730s on the rear of my car, while keeping my half-worn RE-71s up front. Honestly, it doesn't cost anymore money (just time) to go back and replace the fronts, if you can't tolerate the performance. You just need to be smart enough to not push the car too hard while evaluating the car's handling with the mixed tires (just like you do after installing new tires). And, besides being cheap, I wanted to experience first-hand how a 964 handles with mixed front/rear tires.
Now, my car (and probably your own) always handles a bit flaky immediately after new tires are installed. However, it's been over 1k miles since the new RE-730s were installed, and I'm still not happy with how the car's front-end feels at freeway speeds. And, the back-end feels too squirrely. So, it's time to bite the bullet, and order up a set of RE-730s for the front. Experiment over.
Here's a link to a relevant thread from the 993 board:
<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=3&t=003101&p=" target="_blank">Mixing Different Tire Models?</a>
Also, I believe Steve Weiner goes so far as to recommend that you replace all four tires whenever you buy new tires, regardless of whether you'll be installing different model tires, or how much tread may be on (for example) the front tires. Unfortunately, I was unable to locate the thread where I remember Steve W. making this recommendation.
07-04-2002, 08:08 PM
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That latter comment regarding replacing all four tires regardless of condition doesn't make any sense. Yes there will be initial handling changes until the new ones are scuffed in. Considering the fact that front and rear tires wear at markedly different rates AND are not rotatable front and rear (thus evening out), 911's are always running with differing tread depths.
Weiner says a lot of stuff that people tend to just take on faith. He's just a guy with a website.
Weiner says a lot of stuff that people tend to just take on faith. He's just a guy with a website.
07-04-2002, 08:17 PM
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>Yes there will be initial handling changes until the new ones are scuffed in. Considering the fact that front and rear tires wear at markedly different rates AND are not rotatable front and rear (thus evening out), 911's are always running with differing tread depths.
My sentiments exactly ....
My sentiments exactly ....
07-04-2002, 08:56 PM
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I'm w/ Steve W. on this...
there is a right way to do things & a cheap way to do things. rarely are they the same, esp. w/ Porsches. It is certainly justifiable to look for tolerable compromises that save $s, but don't delude yourselves that it is also the "best performing" course of action. As a pro, Steve can't justify anything but advising the best way - customers then do whatever they want. Liabilty exposure on tire issues for any auto service business is pretty high these days.
I have gone through this tire-mixing experience (& have talked w/ others who have had the same). W/ all RE71s my '87 Carrera was fine. Then I mixed new RE730s (rear) w/ the old RE71s (frt.) for the usual reasons; saving a $ & trying to "equalize" the frt-rear wearout, so next time I can replace them all together if I wish. What a mess! nervous, unsettled - everything people note (yes, AFTER the break-in period). After new frt RE730s (& broken-in) all is nice & stable again.
Buy your ticket & take your chances...
there is a right way to do things & a cheap way to do things. rarely are they the same, esp. w/ Porsches. It is certainly justifiable to look for tolerable compromises that save $s, but don't delude yourselves that it is also the "best performing" course of action. As a pro, Steve can't justify anything but advising the best way - customers then do whatever they want. Liabilty exposure on tire issues for any auto service business is pretty high these days.
I have gone through this tire-mixing experience (& have talked w/ others who have had the same). W/ all RE71s my '87 Carrera was fine. Then I mixed new RE730s (rear) w/ the old RE71s (frt.) for the usual reasons; saving a $ & trying to "equalize" the frt-rear wearout, so next time I can replace them all together if I wish. What a mess! nervous, unsettled - everything people note (yes, AFTER the break-in period). After new frt RE730s (& broken-in) all is nice & stable again.
Buy your ticket & take your chances...
07-04-2002, 10:00 PM
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A corollary to the discussion is that when you do buy 4 new tires, buy the newest/latest (not when the tire was made, rather, when the tire "model" was introduced) tires that make sense for your intended usage. That increases the chances that in 4 years they may still be available when it's time to replace the rears.
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07-05-2002, 04:34 AM
#8
Joh
I think a summation would be: 'John, it's time to open that wallet'.
Don't forget to switch off the alarm.
<img src="graemlins/icon107.gif" border="0" alt="[icon107]" />
I think a summation would be: 'John, it's time to open that wallet'.
Don't forget to switch off the alarm.
<img src="graemlins/icon107.gif" border="0" alt="[icon107]" />
07-05-2002, 05:22 AM
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Ermmmm...
Have you checked your tyre pressures??
What you describe is much the same I felt when I replaced my rear tyres a few months ago, a very twitchy and nervous car.
It was all down to the tyre fitter having inflated them up to 50psi as opposed to the standard 36.
First check this, then look at the rest.
Have you checked your tyre pressures??
What you describe is much the same I felt when I replaced my rear tyres a few months ago, a very twitchy and nervous car.
It was all down to the tyre fitter having inflated them up to 50psi as opposed to the standard 36.
First check this, then look at the rest.
07-05-2002, 05:32 AM
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Dear Riccardo,
It is a good idea to check tyre pressures but you cannot get past the simple and proven fact that you cannot mix and match tyres on a 911, certainly not a 964 of any type and not have an adverse affect on handling.
Some of us actually went out deliberately and tested this. I still remember the fun we had changing wheels and tyres at my mechanics and playing around. Certainly got up a sweat on those days. I also tested mixing and matching on my daughters 944, just for fun. I wrote up a couple of magazine articles on this subject.
Mix tyres and you will have handling problems and there is nothing you can do about it until the other tyres are replaced,
Ciao,
Adrian
911C4
It is a good idea to check tyre pressures but you cannot get past the simple and proven fact that you cannot mix and match tyres on a 911, certainly not a 964 of any type and not have an adverse affect on handling.
Some of us actually went out deliberately and tested this. I still remember the fun we had changing wheels and tyres at my mechanics and playing around. Certainly got up a sweat on those days. I also tested mixing and matching on my daughters 944, just for fun. I wrote up a couple of magazine articles on this subject.
Mix tyres and you will have handling problems and there is nothing you can do about it until the other tyres are replaced,
Ciao,
Adrian
911C4
07-05-2002, 05:44 AM
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Kevin-
The comment was replacing tires REGARDLESS of whether you are installing different models or not or amount of tread depth left. That makes no sense if the original models are available for replacement. In your case, you mixed models...so yeah you ended up with a squirrely setup. I can't recommend that either. But there is no reason in the world that if you wear out your rears for example, you should replace all four tires with new ones....as long as the original models are used for replacement of the worn ones it shouldn't be problem. That's like saying that at any time you detect different amounts of tread on any of the tires, you should replace the whole set.
Weiner pulled some pretty dicey stuff on my car...I think the "pro" label is hardly warranted. He doesn't even have a shop, although he likes to pretend he does.
The comment was replacing tires REGARDLESS of whether you are installing different models or not or amount of tread depth left. That makes no sense if the original models are available for replacement. In your case, you mixed models...so yeah you ended up with a squirrely setup. I can't recommend that either. But there is no reason in the world that if you wear out your rears for example, you should replace all four tires with new ones....as long as the original models are used for replacement of the worn ones it shouldn't be problem. That's like saying that at any time you detect different amounts of tread on any of the tires, you should replace the whole set.
Weiner pulled some pretty dicey stuff on my car...I think the "pro" label is hardly warranted. He doesn't even have a shop, although he likes to pretend he does.
07-05-2002, 06:20 AM
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Thanks for all responses - interesting comments by all really. Will replace fronts at end of the month (£1k main service still hurting wallet!!). Still VERY surprised at the completely different characteristics after installing new rears. Can't get my head around the theory (slightly larger diameter, a bit more grip, but why front end handling so different???).
I would love to hear, or be pointed to, some theoretical analysis of HOW new rear rubber can compromise handling this much. I concede there is a clearly defined change in my cars stability - from rock solid at 120 mph to vague at 80 mph - but why??????
<img src="confused.gif" border="0">
I would love to hear, or be pointed to, some theoretical analysis of HOW new rear rubber can compromise handling this much. I concede there is a clearly defined change in my cars stability - from rock solid at 120 mph to vague at 80 mph - but why??????
<img src="confused.gif" border="0">
07-05-2002, 06:35 AM
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John, did you check the pressures then??
Adrian, I agree with you, but I guess what tyres you're using make a difference. When I bought my car it came with new S02s at the front and worn P7000s at the rear. I kept this setup for another 3000kms and the car never felt 'squirelly' or anything like that. Keep in mind I don't take it on the track. It did wonder a bit at high speeds, but that was cured with a new alignment.
Having said that, it does feel better now that I have bought S02s for the back as well.
Adrian, I agree with you, but I guess what tyres you're using make a difference. When I bought my car it came with new S02s at the front and worn P7000s at the rear. I kept this setup for another 3000kms and the car never felt 'squirelly' or anything like that. Keep in mind I don't take it on the track. It did wonder a bit at high speeds, but that was cured with a new alignment.
Having said that, it does feel better now that I have bought S02s for the back as well.
07-05-2002, 06:43 AM
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Yeah Riccardo
I checked pressures before the new tyres & after. I set fronts to 36, and deflated my old rears down from 46 to 42.
New tyres have been set and checked the same.
I absolutely convinced that I'm not imagining the change in handling - the other week I got up to 125 MPH before it started to feel a bit vague, so I backed off. Yesterday, 80 on the ring road felt just as bad!
I will be having the car checked next week for sway bar mounts etc, just to make sure everything is pucker.
I am also going to price up some lowering springs, as the attitude of the car seems all wrong - distinctly nose up. Ive got about 2.5" clearance at the front between top of tyre and wheel arch and only 1" at the back. I'm not overly worried that it looks a little odd (964's look great anyway!), but if lowering will improve high speed stability, I'm all for it.
I checked pressures before the new tyres & after. I set fronts to 36, and deflated my old rears down from 46 to 42.
New tyres have been set and checked the same.
I absolutely convinced that I'm not imagining the change in handling - the other week I got up to 125 MPH before it started to feel a bit vague, so I backed off. Yesterday, 80 on the ring road felt just as bad!
I will be having the car checked next week for sway bar mounts etc, just to make sure everything is pucker.
I am also going to price up some lowering springs, as the attitude of the car seems all wrong - distinctly nose up. Ive got about 2.5" clearance at the front between top of tyre and wheel arch and only 1" at the back. I'm not overly worried that it looks a little odd (964's look great anyway!), but if lowering will improve high speed stability, I'm all for it.