hi everyone.

My B310 was running with a15, 5 speed 60 series and h150 3.7 diff. 13" performance spitfire. 175/70/13 tire.
But the diff made humming noise and i replaced it with h150 4.11 diff.

now i feel like not enough gears. engine revs higher for the same speed. but its fun to drive within city. better acceleration.

my question is what is the difference i will feel if i change my wheels to 15". in term of acceleration, top speed and handling.

*p/s: my twin su and 4-1 extractor still pending for installation.

Nothing will happen, if you fit 155/60R15 -- it will not change the gearing but 1%. By the way 175/70R13 was factory optional size for B310 and with a 4-speed the top speed was 150 kph ...

Another way to look at it:
* 3.700 final gear with 175/70R13 tires
* 4.111 final gear with 185/70R15 tires
is about equal gearing

Compared to 3.7 with 13", either combination will lower RPMs at any given speed and increase fuel economy, the downside is reduced acceleration

If you have the B310 A15 engine (80HP), top speed will be made in fourth gear. So you got plenty of revs even with the small gears & tires. If you have a Vanette A15 (67HP) top speed will will be made at approximately 5200 RPM

185/70R15 is nominally 25.4" tall, although that number will vary somewhat depending on wheel width, tire pressure, model of tire, etc.

http://www.advanced-ev.com/Calculators/TireSize
5200 rpm x 25.4" tire x 4.11 diff = 95.6 mph
5200 rpm x 22.7" tire x 3.70 diff = 94.9 mph

That's fairly close to the same effective gearing. It will take maximum HP of the A15 to get to that speed, which means revving it up all the way. You'll run out of revs in fifth gear, but in fourth gear it should go all the way (if you have enough room to get it up to speed). Although I'm not sure if the 67 HP version has enough power to push through the air to 95 mph, the 80HP version does

Thats very useful info...

With 185/70/15, will my handling improve?

Btw, my engine is B310 A15 egi block + c22 head + temporarily a12 carb and a12 exhaust manifold

Ah, that has the good camshaft. Once you get the SUs and extractors the higher RPMs should wake up

185/70R15 might help handling compared to 175/70R13 as it is 10 mm wider. On the negative side, the sidewall is taller. Most importantly keep the air pressure appropriate, start with Nissan recommendations -- not too much air, but even more important not too little air

The 15 inch wheels will likely have a small detrimental effect on the handling; you'll end up with the car riding 19-20mm higher. Additionally the steering will not feel as direct with the taller tires as they'll be more "wind up" (delayed deformation of contact patch) in the tires. Also the 15" wheels and tires are going to wiegh more and it will take more power to speed them up (think 4 giant flywheels).There is one benefit to the larger wheel, the ride over rough pavement will improve.

So basically the car will corner slower, have less direct steering feel and accelerate slower BUT the difference may be small enough that you're willing to trade that for the better ride over rough pavement. For instance here in Las Vegas the roads have lots of sharp edged pavement seams, this is why I drive a Subaru Outback with tall tires, rather than an Imprezza with low profile tires.

Tom

Tom

since i couldnt find the twin su heatshield, i managed to home make one. pls comment. pls advice if its usable.

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any advice for the heat-shield? do i need to make another one...?

I think that one should do the trick.

Tom