Po długiej jeździe bolą mnie ręce, jeśli kierownica jest za wysoko.

Because po here means after, and in that meaning it takes the locative case.

So:

• jazda = ride, driving, riding
• po jeździe = after the ride
• po długiej jeździe = after a long ride

Both długiej and jeździe are in the locative singular because they belong together.

Compare:

• długa jazda = a long ride
• po długiej jeździe = after a long ride

Because adjectives in Polish usually agree with the noun they describe in:

• gender
• number
• case

Here the noun is jazda, which is:

• feminine
• singular
• locative (because of po)

So the adjective must match:

• długa jazda → nominative
• długiej jeździe → locative

This is a very common pattern in Polish noun phrases.

Because the grammatical subject is ręce (hands), which is plural.

In Polish, the verb agrees with the subject:

• boli ręka = the hand hurts
• bolą ręce = the hands hurt

So in this sentence:

• ręce = subject
• bolą = plural verb form

Even though English says my hands hurt, Polish structures this more like hands hurt me.

Because mnie is the person affected by the pain.

Polish often expresses this idea with:

• the body part as the subject
• the person as an object pronoun

So:

• bolą mnie ręce literally works like the hands hurt me

This is why you get:

• boli mnie głowa = my head hurts
• bolą mnie nogi = my legs hurt
• bolą mnie ręce = my hands hurt

Here mnie is the accusative form of ja.

Yes, you can, and it is very natural.

Both are possible:

• bolą mnie ręce
• bolą mi ręce

Very roughly:

• mnie can sound a bit more emphatic or more directly focused on me
• mi is the unstressed dative form and is also very common in everyday speech

In many situations, both versions are acceptable. A learner will hear both.

Because ręce is the grammatical subject of bolą.

In Polish pain expressions like this, the body part is often the subject:

• ręce bolą
• głowa boli
• kolano boli

So:

• ręce = nominative plural
• bolą = agrees with ręce
• mnie = the affected person

This is different from English, where we often think of I as the main subject in my hands hurt.

Ręce can mean either hands or arms, depending on context.

Polish often uses:

• ręka for the whole upper limb
• dłoń more specifically for hand/palm
• ramię for arm/shoulder area

In this sentence, because of kierownica and a long ride, ręce would most naturally be understood as hands/arms in a general sense.

It can mean either, depending on context.

• in a car: steering wheel
• on a bicycle or motorcycle: handlebars

Because the sentence mentions a long ride and hand pain from the height of the kierownica, many learners would understand this as handlebars. But the word itself can also mean steering wheel.

Context tells you which meaning is intended.

Za wysoko means too high.

Here:

• wysoko = high
• za wysoko = too high

In Polish, za before an adverb or adjective often means too in the sense of excessively:

• za duży = too big
• za drogo = too expensive
• za szybko = too fast
• za wysoko = too high

So kierownica jest za wysoko means the handlebars / steering wheel are too high.

Because Polish often uses an adverb like wysoko with być to describe position or setting.

So:

• kierownica jest wysoko = the handlebars/steering wheel are high
• kierownica jest za wysoko = they are too high

If you used wysoka, that would be an adjective agreeing with kierownica as a noun, but in this kind of sentence Polish very naturally uses the adverbial expression jest wysoko / nisko / za wysoko / za nisko.

This is especially common when talking about position, placement, or adjustment.

Yes. Jeśli and jeżeli both mean if.

In most everyday situations, they are interchangeable:

• jeśli kierownica jest za wysoko
• jeżeli kierownica jest za wysoko

Jeśli is often a little more common in everyday speech, but both are correct.

Yes, the word order is natural, but Polish word order is fairly flexible.

The given sentence:

• Po długiej jeździe bolą mnie ręce, jeśli kierownica jest za wysoko.

You could also hear variations like:

• Jeśli kierownica jest za wysoko, po długiej jeździe bolą mnie ręce.
• Bolą mnie ręce po długiej jeździe, jeśli kierownica jest za wysoko.

The basic meaning stays the same, but word order can shift emphasis:

• starting with Po długiej jeździe highlights the time
• starting with Jeśli kierownica jest za wysoko highlights the condition
• starting with Bolą mnie ręce highlights the result

You can, but it changes the feel.

• bolą mnie ręce = my hands hurt
• bolą ręce = hands hurt / the hands hurt

Without mnie, the sentence becomes less personal and less specific. It may sound more general or more context-dependent.

If you want to clearly say that your hands hurt, keeping mnie is best.

The dictionary form is jazda.

The form jeździe is the locative singular form.

This kind of vowel/consonant change is normal in Polish inflection:

• jazda → jeździe

You do not need to predict every change perfectly at first; it is something learners gradually get used to by seeing many examples. The important thing is to recognize that jeździe belongs to the noun jazda.

Most naturally, it sounds like a general statement:

• After a long ride, my hands hurt if the handlebars are too high.

That is because jeśli often introduces a general condition, and nothing in the sentence limits it to one specific event.

If you wanted a very specific one-time event, context would usually make that clear. As written, it sounds like a general observation about bike fit or riding position.