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Drag Tyre Experts Opinion - Slick Walk? ET Drag vs Radial

Drag Tyre Experts Opinion - Slick Walk? ET Drag vs Radial

Author
Discussion

ChrisPackit

Original Poster:

42 posts

45 months

Wednesday 14th June
quotequote all
Guys

Hoping someone with considerable drag racing knowledge will be able to answer this question!

So I've been building a little Mazda MX5 for the last 5 years with its sole aim of drag racing, and has been on the Strip for the last year with reasonable success. Last season it was putting out about 420hp and transferring the power through a pair of M/T ET Drags (bias ply I understand) with a best time of 11.5 @ 125mph. What I've noticed about the tyres is that early on in the day when the tyres are cooler, the car drives quite straight and as the day goes on and the tyres are warmer Im assuming, the car is now at the point where it's swerving at the top end of the track and quite unnervingly. Reading the Net about this issue, it seems plenty guys have experienced what I believe is 'Slick Walk' where the soft sidewall of the rears wants to move around and the hard sidewall of the Front Radial tyres tries to grip. I've tried playing around with rear tyre pressures from 12psi to 25psi and it's definitely better the higher you go, but still far from perfect. I've also got the car setup up hard front and rear on the suspension which helps to make it more stable.

I believe my 2 options are either a) replace the fronts with a 'Skinny' bias ply tyre, or b) replace the ET Drags with some Drag Radials. I'd be interested to know some real world answers about whether this mix of tyre could be causing this issue, and whether going to a Drag Radial would be a wise move to make the car steady at higher speeds.

I have another 100hp this season which is completely unusable as it is. I had 2 close calls at Shakespeare this weekend, with one ending up on the wrong side of the track at the end of the 1/4, and the other resulting in a tank-slapper at 120mph and was lucky not to be in the wall - This makes me think I need to address this properly and urgently!

Thanks for any advice!

Chris

Flying Phil

544 posts

67 months

Wednesday 14th June
quotequote all
Given the range of rear tyre pressures that you have tried I would suspect the aero factor could be the culprit at the top end (But the cooler morning is peculiar??). Are you running with the windscreen? do you have a flat (ish) plate boot spoiler? Do you have a front splitter /air dam?

Turn7

13,582 posts

143 months

Wednesday 14th June
quotequote all
http://www.websterraceengineering.co.uk/


wink


Seriously...
Now right by the gates to the Pod as well....

ChrisPackit

Original Poster:

42 posts

45 months

Thursday 15th June
quotequote all

Thanks for the replies, though Im not convinced it's aero - In answer to your questions... Yes it has a windscreen, no boot spoiler and no front splitter, so there is room for improvement in the future. I just can't see how they would make a big difference to the stability of the car when other MX5 with less power are more stable and on road tyres.

Maybe a call to John Webster is the answer then!

Cheers

Tet

1,189 posts

126 months

Sunday 18th June
quotequote all
The correct answer here is "speak to someone that knows". Although there are others, the two prime candidates in the UK are Jon Webster and Andy Robinson. Maybe your problem is chassis related. Maybe it's suspension setup. Maybe it's tyre choice (although I doubt it). Whatever the cause, either of those two should be able to give you the answers you need. They're not cheap (I've paid Jon a small fortune already, with more likely to follow). But you get what you pay for, and I couldn't be happier with the work.
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