My Fireblade now has 185/60R13 soft tyres. This is truly great for city and track, reaches 110 mph at 11000 rpm. I have been traveling with them, usually doing steady 80 mph at about 8000 rpm. I'm considering buying a set of cheap bigger wheels for journeys only. That way I don't need to travel on slicks (somewhat stupid) plus I lower my steady rpms.

I was thinking something like 80 mph at about 7000 rpm. The reason for this choice is that both 80 mph and 7000 rpm look like reasonable figures for steady highway cruising.

My problem is that the resulting wheel sizes are somewhat huge compared to the original. Also these bigger diameter wheels usually come in wider footprints only. I can see how any benefit in fuel consumpion associated to dropping rpms is then compensated by an increased overall weight of the car plus increased wheel footprint. Still I think it may be good for engine wear, what do you think?

So my question is: am I going too big? Should I go for smaller wheels, say 7500 rpm at 80 mph or something? Or is my choice of 7000 rpm at 80 mph a sensible one?

My choice of 7000 rpm at 80 mph gives the results in the attached pic (lousy Excel calc). I don't know which of these exist and which are common (ie cheap), obviously the resulting profiles need to be rounded in steps of 5.

Comments?

Cheers,

Alex

PS: the wheels fit nicely in the arches, that's not a problem
Rescued attachment tyres.jpg

hi i have 195 55 15 wheels with a 3.62-1 diff this gives about 6500 rpm at 80

and still sub 4 seconds on acceleration

195 50 15 tyres tend to be a bit cheaper than 195 55 or 195 45

The overall diameter of Andy's tyres is 596 mm and the resulting gearing is longer than mine by A LOT (he gets 6500 rpm where I'm getting 8000!!). So the rpm figures I was considering are not stupid, it's just I may need to think about changing my diff ratio

BTW Andy, have you actually MEASURED sub-4 secs with a standard Fireblade engine and those ratios? It sounds like a very good figure, how much does your car weigh? What's your diff (open / LSD) and rear suspension setup? Road tyres or slicks?

Cheers,

Alex

real figures are,on yokahama road tyres,0-60 3.7 seconds(timed at tuning japanese after rolling road tune) top speed 137.4mph(gps timed at the sme company)

the diff is open,no lsd(as this causes drag)
total weight of car at test 418kg wet

suspention is double wishbone with protech shocks all round

and in the words of ian hyne(kitcar magazine) "the gearing on this car is spot on,the gear changes come in equal lunges up the box "

hope that helps

Andy, is that Tuning Japanese in Aldershot? If so would you recommend them as they are local to me and i'll need to get mine on the rollers soon.

How did they measure the accceleration / speeds, on the rollers?

Chris

not mesured on the rollers i had it tested after the tuning session on private road

yes highly recomend them,the man you need to speek to is paul

they aint cheep thow my session including a dyno jet kit was not far short of £500

Ouch how come it was so much, thats ~£400 labour so it must have taken them an especially long time on the rollers or something?
Im also concerned that although they sell Dynojets, Im not sure how well they know Power Commanders for FI bikes, so I think PDQ in Slough might be a better bet if TJ are that expensive too.

they had the car for a week,not to work on for that long,just i could only drop off and pick up on a saturday

as the name sugests they specialize in jap engines,car and bike
they know all about power comanders and that

but as isaid very dear

Sounds like they might have charged you storage too
I'll give TJ a call to see how much it will but what youve said has put me off a little, there's another one nearby, surreyrollingroad.co.uk in Camberley so I might give them a call too.

cheers

Chris

Cheers Andy, I'm very impressed, What is your engine?? Fireblade? What year? Tuned or standard?

I'm very impressed really!

Also I wonder why my car weighs 460 kg wet and yours is a mere 418.. I don't think yours can have a lot less stuff than mine, I have nothing there

Congrats, your little car is a winner!!

Cheers,

Alex

wieght,well thats MNR for you,as to engine its a 1997 rrv fireblade with a pipercross filter and a stage 2 dyno-jet kit,thats it apart from that its standard

Congrats!! Fantastic figures, I have the same engine ('97) although I know nothing about dyno jets.. one more thing to learn sometime in the future..