Kumho V70 grip...

[skydragon]

Question for those with significant experience of using Kumho V70's

 

My car is fitted with soft compound 215 V70's all round and appears to have a lot more grip than when previously fitted with Bridgestone 539's when used on the road (as you might expect).

 

I competed yesterday at Harewood Hillclimb, the first time I'd used these tyres in competition, it was cold (8 deg C) and windy, but dry.

 

I found that when they are stone cold, they don't have a lot of grip, in fact they appear to have a lot less grip than the 539's which really suprised me.

 

Off the start line, wheel spin seemed to be unavoidable (unless you just moved away slowly) and the first corner was a whole world of understeer.

 

My 64ft times yesterday, were 0.4 secs slower than last year when I had 60bhp less power and list 1b tyres (539s)!

 

Half way around the Hillclimb and the grip levels started to kick in and by the end everything was just fine....

 

At first I thought it was just me, but speaking to other competitors there who were also running Kumho V70's they were having exactly the same problem, especially off the start line and into the first corner. Most peoples 64ft times were 0.3-0.4 secs slower than last year on list 1b tyres Changing start line technique or tyre pressures seemed to do little to alter the situation.

 

With the wind and low air temp, even warming the tyres up in the warm up area didn't help as it was then 30 - 40 secs until you actually started, by which time the tyres were stone cold again in the cold wind.

 

Is this a case of this is just how they are when cold?

 

Do they behave totally differently when the air temp is 17-18 deg C, or is it a case of they just have poor grip until warmed up?

 

( i ended up using 15psi on the fronts and 16 psi on the rears, but also tried a number of higher/lower combinations)

 

1.6 K Series EU3, 2003, with DVA K05 and a few other goodies...

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[robmar]

Skydragon - where they new tyres you had fitted 🤔 from expereince they need quite a few heat cycles through them to be ok from cold, this is especially true for the fronts as it is harder to get heat into them.

 

Also a lot will depend on your setup having changed tyres you may want to consider what else could be changed.

 

I think you will also find getting a more powerful car off the line quickly a lot harder to do... and you can easily light up the rear tyres, and you probably have to do some testing to work out the optimum start line technique for your setup

 

As a comparison to 539's I would really expect them to have more grip at all times to be honest but it has been a long time since i ran 539s...

 

 

[skydragon]

Hi - Yes they are new tyres, although I've probably done about 500 miles road use with them and a (short) trackday. So they have been cycled a few times.

 

Also a lot will depend on your setup having changed tyres you may want to consider what else could be changed.

any guidance?

 

Agreed ref starting technique, but there are other (far better drivers than me) who have moved over from 1b stunners to 1a Khumos and who are having exactly the same issue...

 

 

 

 

[Shaun_E]

The startline at Harewood is concrete and grip varies considerably depending on the conditions. You need to get some heat in the Kumhos to get them to grip - a good burnout helps. I (and others) regularly get 64 feet times around 2.2 seconds or less.

Set-up wise you need at least 2.5 degree negative camber on the fronts.

 

 

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