Speed on KH straight

[DJ]

Was getting frustrated on Tuesday night as was only hitting 95 on the straight just after the bridge but was getting between 100 and 105 last time out of my wee 156bhp S2. Remembered afterwards that the roof was on last time (Feb) and there being some posts about this. Dug the following quotes out from the Glenrothes Poll post by AndyG and wondered if this was ever tested again by those in these quotes? I experienced a 7 or 8 mph drop but seems a lot though for just having the roof off. Like Neil, car felt exactly the same, not down on power. Guessing air would be cooler/denser in Feb but again seems too much of a loss. Picking at straws now...

If no conclusion yet or any other thought from anyone else, I might test this at Tuts evening on the 6th....... and put up with the 'roof on' jibes for a few laps no doubt.

Neil

Were you driving the exige without the roof?

That was me. I'm not sure if I'm imagining things but the roof off seemed to knock a good few mph off my top speed down the main straight. Was getting just over 100 and I'm sure I've managed 110 in the past.

Neil

Were you driving alone? I've noticed slower speed during pax laps (as expected) but not as much as 10mph.....

Mass

I had a pax but I've had a pax before. Will need to take the roof with me next time and try with it on and off to see if theres a difference

Neil, I think what Andy is saying is that you should get to more speed than you were getting before the (mortals') usual braking point. Your engine could be down on power. Does the engine feel different in any other way? I don't think "No roof" would affect the top speed at KH much anyway as the speed is relatively low.

Neil, I think what Andy is saying is that you should get to more speed than you were getting before the (mortals') usual braking point. Your engine could be down on power. Does the engine feel different in any other way? I don't think "No roof" would affect the top speed at KH much anyway as the speed is relatively low.

tyre pressure should just make them grip better mate, and if anything they should enable you to carry more exit speed leading to a great speed on the straights not lesser

Happy to grab a pax next time and see if it feels down on go - although hopping from the Atom might not give me the most objectove view point

Mass
The engine doesnt feel any different to what I remember. Thinking about it though, the last time I had my tyre pressures far too high - wore out the centre of my rears. This time I dropped them to 22F 24R once they were warmed up. Could the tyre pressure difference explain it?

tyre pressure should just make them grip better mate, and if anything they should enable you to carry more exit speed leading to a great speed on the straights not lesser

Andy

I'm pretty sure I was quicker through the bends this time - less of a queue behind me! I'll take you up on the pax offer.
Cheers

Happy to grab a pax next time and see if it feels down on go - although hopping from the Atom might not give me the most objectove view point

Your straight line speed is determined by the corner exit speed, grip level and the acceleration available. High tyre pressures could cause the wheels to spin at lower speed losing the exit speed. As Andy mentioned, the lower tyre pressures you had would have given you a better drive out of the corner. So long as your engine is giving you the same level of power, you should have reached at least the same (if not higher) top speed....... This is why I asked about the engine.

May be an idea to get a pax on a NA exige and compare the feel of the engine.

[mac]

perhaps since it was never fully dry (just a drying line) you weren't getting the same exit out of the hairpin?


Mac

[tut]

You will always see the serious Elise racers with the roof on, in most cases with a hardtop, often in carbon fibre.

There is a 5-7mph difference on a standard Elise between on and off when flat out.

tut

[DJ]

Other way round Mac.

Feb = roof on. Freezing cold, damp to start with but drying line that quickly became fully dry. Managed 100 - 105 on straight.
This week = roof off, nice evening and dry track but only getting 95. Also with another session under my belt I thought I was exiting the hairpin a bit faster.

[mckeann]

Other way round Mac.

Feb = roof on. Managed 100 - 105 on straight.
This week = roof off, but only getting 95.

Thats what tut is saying, most racers had the roof on for less drag at high speed. I used to chop and change depending on wether it was sunny or not

It is a big difference, but cold weather and the roof will make your car faster. As long as its as fast as other cars then it doesnt matter.

[mac]

Other way round Mac.

Feb = roof on. Freezing cold, damp to start with but drying line that quickly became fully dry. Managed 100 - 105 on straight.
This week = roof off, nice evening and dry track but only getting 95. Also with another session under my belt I thought I was exiting the hairpin a bit faster.

Ah - so you weren't talking about the SIDC day as being the May event.

Mac

[Shug]

Are you consistent enough yet to be getting the same exit out of the hairpin each time you go to KH? IMHO it makes a sh*tload more difference than whether the roof is on or not. You get 5mph more on exit, you carry that 5mph all the way up the straight, as you're nowhere near terminal speed in an Elise by the end of the KH straight. Sometimes I visit the place and I'm really in the groove, sometimes I just don't hook up for the whole session - things like tyres make a difference to your turn-in & exit to the hairpin too.

[mac]

Following on from what Shug said - if this is your second trackday it's far more likely that your carrying a bit more speed into the hairpin but comprimising your exit.


I've only just started getting a decent exit on a regular basis and I've done a LOT of trackdays in the last six year!



Mac

[Sanjøy]

When was the last time you cleaned your airfilter ?

[Andy G]

the other thing could be the speedo.

My S2 dials used to move around everyonce in a while. Might be worth checking if its reading anything at 10mph.

My 111r used to over read by about 10mph every so often, and rev counter would recalibrate wrongly - although some might argue that my car did get revved to the wrong side of 10000 rpm

Exit speed is key though, and think the drag of the roof will really start to be a big factor around 100 or so. Interestingly i got told inthe LOTRDC last year that they wanted to check my car for power, as there was a suspicision i had too much from some of my competitors.

Turns out that after Brands i was running at 160bhp and down on where i should have been. One of the chaps complaining actually had 180 bhp, but if you carry speed through the corner ............

[GregR]

Is the rest of your lap so hooked up that a 5mph difference on the straight is the only thing annoying you? I have to confess, I hardly look at my speedo at all when I'm on track.

Woulodn't worry about it mate. If the sun's out and the track's dry I'd wager you'll have far more fun with the roof off and 5mph less on the straights than if you were cooking inside the cockpit

[DJ]

I'm definitely not consistent out the hairpin - or anywhere else ! - as still quite new to trackdays. Was my fourth time on track with the Elise and only done this a couple of times before with other cars.
I'm just looking to keep learning and hopefully improve. Actual top speed on straight is of little interest but it was the relative 6/7 mph less made me think I was going backwards until I remembered about this roof on/off post and wondered if it it had been tested any further.

Seems a few think this may be a reason or factor, but the posts on exit speed have got me thinking too. Definitley entering the hairpin faster as the pagids and more experience have given me a bit more confidence to brake later, but I could be taking more speed off and compromising the exit.

Brand new Hurricane put in just 1200 miles ago Sanjoy so should be OK.

Will test the roof on/off thing back-to-back on 6 June just to see how much of a difference this makes. If any of the more experienced guys are giving their cars a rest for a few minutes on the 6th and wouldn't mind jumping in beside me for a lap or two for some pointers, would be greatly appreciated .

thanks to those who have posted replies

[Modena Scotland]

Hi DJ

I don't think the top speed at KH is affected by the roof on/off too much as the straights are not long enough (the two straights have the same top speed on the Exige S which is about 110 mph). IMO, the exit speed will affect it far more. Going into the hairpin too hot will cause understeer which will force you to take a corrective action (either ease off the throttle to regain grip or make the car to oversteer to get back onto the desired line) which will lose speed carried. ie slower exit speed. Its more important to get into the corner slower and exit faster than vice versa, if improving the lap time is your goal.

See you on the 6th.

Cheers

Mass