Down Gearing??

[wallya1]

G'day guys,
I just wanted to know, at what maximum speeds is it safe to shift down a gear on an e30 Sport. Reason I ask is that i don't want to be blowing a gear box by trying it at speeds unreasonably high. For example from 4-3 or 3-2 or 2-1 etc..

Best Regards,
Wally

[mrLEE30]

this depends on your rear diff ratio, but it suffices to say if you drop your clutch out and the tachometer rises anywhere near the red line or higher then you will over-rev the engine mechanically - by that i mean provided the rear tryes grip enough the engine has no choice but to revolve at the speed of the tyres through the gearbox, this could mean the engine turns much faster than its design and this usually causes broken crank/rods etc etc.

a general rule of thumb is see what speed you can achieve in each gear on the way up, in this case you are accellerating and thus the engine will be limited electronically and will not be allowed to turn faster then its design speed (assuming you have not played with the cars ECU etc), so it means you can safely down shift at this speed.

downshifiting too early (and i speak from our experience) will damage your engine, we have customers break 2 or 3 engines on our track Caterhams a month like this. normally catastophic failures such as rods put through the engine casing etc.

Finally the next time you go and watch a race (of normal cars not F1 things) and you will hear the engine revving on downshift, this is called rev-matching or heal and toe, the idea is you break and as the clutch is let out for each downshift sequence the throttle is revved (with the side of your foot still on the brake pedal) this allows the engine to get up to speed before or as the clutch is let out allowing for a smoother downshift, less strain on the drive train and 100% reliance on the brakes for braking not the engine.

hope that helps

mrlee

[DHFiS]

If you dont blip the throttle on downshift the syncromesh will not be able to engage the gears when input and output are at wildly different speeds.

[mrLEE30]

thats the idea of a syncromesh!! to syncronise the two different speed parts by use of a cone clutch/baulk ring.... its older gearboxes without these that require more attention during down shifting...... dont let Brian moooore hear you are suggesting a BMW (or Getrag) gearbox requires throttle action on the downshift!!!

mrlee

[siddiqi1]

great thread! ive always wondered this myself! i occasionally drop from 4th to 3rd and have had a habit for long time now of blipping the throtle; but what would happen if you went from say 4th straight to second?

[wallya1]

I'm assuming at low speeds, 4th to 2nd isn't too much of an issue, provided you're not exceeding the normal speed you would reach in second gear?...

[gooner1]

Iv,e always blipped the throttle when changing up from 2nd to 3rd gear too , was told many years ago that this change of gear puts the biggest strain on the clutch. Not sure if its true tbh, but it,s just a natural reaction now.

[wallya1]

Cheers for the insight lee. So if one can reach 60mph in 2nd gear, you're telling me that its perfectly safe to shift from 3-2 at this speed??

[wallya1]

And sorry Lee, but why does the foot have to be on the brake pedal when blipping the throttle in heel and toe? Can it not be blipped without engaging brakes?

Cheers

[siddiqi1]

thanks for the advice there! ah yes thats what i do; if you're trundling along in fourth and suddenly feel the urge to show the saxo he needs to calm down, then i blip down to second!

but O/T, my bro-inlaws e60 m5 blips the throttle on downshifts itself, you can drive all the way down the a3 in fourht and just shift down a gear and it blips it so loud and bang in second, but obv thts a smg and all that double clutch palawa!

with regards to the brake toe and heel; thats only relevant i bleive to racing as you approach a bend, as into prevent the engine from "engine braking" and thus reducing your momentum into the corner; hence using the brake to control the speed and bliiping the throttle into the correct rev range for a smooth gear change and instant accleration out of the bend

[wallya1]

Ahh sweet.. So e30's don't have synchronisers im assuming?
I haven't tried it as yet but I imagine the heel and toe method would be a pain to do every time you want to downshift while maintaining optimal speed to overtake any cars out on the highway..

[siddiqi1]

of course e30s have syncromeshes, syncromeshi, or whatver the plural of that word is!

so no you dont have to heel toe unless you happen to be racing another car and approach a bend, then it may be suitable to do such a thing

[snoops]

I only ever drop into the following gears at the following speeds

2nd - anything up to 50 mph
3rd - anything up to 70 mph
4th - anything up to 100 mph

[wallya1]

Fair enough.. Cheers boys! A final question.. I was having an argument with a mate who reckons there is a certain speed at which you can downshift to first, whereas I tend to come close enough to a complete stop before doing so. Any insight?

[siddiqi1]

im too scared to shift into first; i think it whacks way too much torque thru the clutch to do that safely! but im not an experienced driver so cant really say!

[wallya1]

Snoops, do you refer to downshifting into 3rd at 50mph using normal shifts or heel and toe?? I certainly have never done that at such speeds..

[wallya1]

Cheers Siddiqi its kool. Anyone else??

[Alex]

i was doing some early downshifting last night in me corsa and its now stuck in 2nd gear with a non existant clutch

[oakey]

Its pretty simple really guys. You can downshift to any gear as long as you don't exceed the rev limit in that gear. Obviously its going to wear stuff out quicker and is pointless if you change down to 3rd at 75mph but its do-able.
In my black tech1 I could change to first at any speed below 25/30 but in my new one it wont let me until 10mph or less.

Obviously it's best to equalise the revs you are changing down to to put less stress on g'box etc.

[Brianmoooore]

If you want to practice gear changing, then drive without using the clutch. You need to do a very slow gearchange, where you have to first lift off the throttle to allow the box to slide into neutral, then match the revs to what they should be for the gear that you are aiming for at the speed you are travelling. When the revs are correct, the lever can be pushed lightly into gear.
I've driven hundreds of miles like this in Minis (as the result of failed clutch hydraulics), and a few hundred in BMWs that I've bought and found to be dry of clutch fluid when picking them up.
Teaches you to anticipate other traffic as well, as stop/start driving is rather hard without a clutch!

[wallya1]

So as long as the car allows me to downshift into first, I'm not going to cause damage at around 10mph or less?
This certainly makes life easier than beginning in 2nd gear at these low speeds. Cheers Guys!

BTW: Congrats on the Olympics in 2012. Better put on a good show for us like the Chinese did. Loved these Games!!

Wally

[mrLEE30]

Cheers for the insight lee. So if one can reach 60mph in 2nd gear, you're telling me that its perfectly safe to shift from 3-2 at this speed??

yes

but why does the foot have to be on the brake pedal when blipping the throttle in heel and toe?

because its a technique for smooth braking!! and as explained above its for track use when you are braking hard,

on a track you should never rely on or use the engine to brake, regular road driving is much different

So as long as the car allows me to downshift into first, I'm not going to cause damage at around 10mph or less?

if your gearbox will allow the gear to be selected then the syncroniser has done its job and the baulk ring will allow the selectors to align and hence the cogs to mesh the gear is found - so no it will not cause any damage.......

sorry to say for once i disagree with brian mooore, whilst he is correct in what he describes this will generally lead to excessive wear on the synchromesh and cause damage to the gearbox as it is almost impossible to exactly match the revs.... but he did say push lightly and his cars were already broken so i suppose just this once... im my opinion better to use the clutch correctly thus no engine forces on the syncromesh or gears

mrlee

[Brianmoooore]

sorry to say for once i disagree with brian mooore, whilst he is correct in what he describes this will generally lead to excessive wear on the synchromesh and cause damage to the gearbox as it is almost impossible to exactly match the revs.... but he did say push lightly and his cars were already broken so i suppose just this once... im my opinion better to use the clutch correctly thus no engine forces on the syncromesh or gears

mrlee

I'm not suggesting anyone drives like this as a matter of course, but it's still a driving skill to learn.

[DHFiS]

thats the idea of a syncromesh!! to syncronise the two different speed parts by use of a cone clutch/baulk ring.... its older gearboxes without these that require more attention during down shifting...... dont let Brian moooore hear you are suggesting a BMW (or Getrag) gearbox requires throttle action on the downshift!!!

mrlee

The syncro copes well with gear changes in normal driving but to quickly engage a lower gear whist maintaining high rpm I still suggest its necessary to blip the throttle. At the very least it reduces stress on the syncromesh. In some modern cars it is done automatically but we E30 drivers are entrusted to perform the operation ourselves.

[daimlerman]

Oh boy!! Put some of you lot into an ERF with an Eaton gearbox with a twin splitter and you would be totaly out of your depth.When I drove such a beast(480bhp) for a living,I would use the clutch to get the thing rolling,thenchange gear,up and down the 'box,without touching the clutch at all....just ease the throttle off,move the stick to neutral,ajust the engine speed on the throttle,slide the thing into the next gear,all whilst entering a roundabout and mixing it with morons with no idea what they were doing....

[mrLEE30]

I'm not suggesting anyone drives like this as a matter of course, but it's still a driving skill to learn.

only meant in jest brian

agreed skills of nursing broken cars home is becoming a lost art,

i remember getting my mini through an auction with a no clutch and knackered main bearing... attepmting to look composed while pullin like hell on the gear stick to get it into neutral just as i got uo the ramp, then not crunching on the way down (not so importent once the hammer dropped ) that paid for my flight next day to Cyprus.... no i was not skipping the country

[Simon]

agreed skills of nursing broken cars home is becoming a lost art,

Soo true!

I get to see some of the real silly things people won't drive a car for being a recovery driver.

Those include an inop washer pump, broken door mirror, smashed rear window, and probably loads of other silly things.

Worst thing I've probably done was drive my first car home with no brakes, popped a rear cylinder on a local mountain road.

[ShakeyC]

The key to all this down shifting, rev matching business is LOOKING AHEAD and anticipating what you need to do in good time. There is no point changing down from 5th to 1st for a 1st gear bend 300 yards too early becuase you loose time and the idea of rev matching is to match your FALLING road speed to your rising engine speed whatever technique you use your road speed should be falling as you change down through the gears to avoid an accident through unloading the cars balance let alone damaging the engine which is nothing in the big scheme of things.

There is absolutely no reason to blip the throttle on up changes infact your doing more harm than good, think about it when you change up the revs will fall as the next gear ratio requires less revs for the same road speed. If you blip the throttle as you change up the difference in engine to road speed increases therefore something has to give way so that the road and revs realign to correct amount, usually engine, gear box, clutch and diffs will take the brunt of shock as the speed 'stalls' back down.

[wallya1]

Never tried this double-clutching business before...but I like it!
Only thing is i don't see the need to use the brake (as you do with heel and toe) when I'm downshifting to overtake a car in front of me.

Oh and just in case, what if i accidentally hit the throttle too hard..does it matter if you pop the gear down while still at very high revs?

[Elecblondie]

No need to use the brake when downshifting necessarily, it's just that you tend to downshift under braking. Simply rev matching the downshift from cruising to be in the power band is absolutely fine, no real need to double clutch either unless you're practicing or it's become natural. If you pop the gear down at higher revs then the synchro has to slow the input shaft down rather than speeding it up, not much difference from a normal shift, obviously more revs is more power and when you start doing things wrong using more power you will wear stuff out but it's not like shifting down when you want to shift up.

In case it helps, sorry for teaching grandmas to suck eggs:
The whole point of rev matching is to match the engine speed to the prop speed when changing gear. As long as you know what the new engine revs ought to be you can; raise the engine speed to match it using the throttle while declutched; only on downshifts or wait longer before engaging the gear allowing the engine speed to fall, on up shifts. All this only considers the engine though, the reason for double clutching is that the power train can be seen to be in three sections; engine to clutch - clutch to gearbox - gearbox to road. With the clutch disconnected and the gearbox in neutral the input shaft to the gearbox is freely rotating. What happens therefore is that when you rev match the downshift with the clutch down the engine speeds up but the input shaft slows down, it's very light so slows down quickly. Fortunately it's very light so as you engage the gear the synchro speeds it up again quite quickly but it wouldn't have to if you kept the input shaft at engine speed. So by releasing the clutch in neutral before blipping and then very quickly slotting it into gear (it's light and slows down quickly) with the clutch down briefly you should eliminate any jerk from the shift. When you get it right the gearbox literally sucks the shift in before you've got it there.

[siddiqi1]

^^^^^ very informative, thank you for that!

[wallya1]

Awesome Elechblondie!! Thanx a lot for that

[Elecblondie]

No probs

[Morat]

At the other end of the scale... a 1945 10 ton Leyland "Hippo" with no power steering, clutch or brakes - let alone synchromesh! What a beast

[wallya1]

Cheers guys! Awesome insight!